The overall goal of this project is to test the hypothesis that increased lysyl oxidase (LOX) expression and activation triggered by high glucose/diabetes compromises basement membrane (BM) function and thereby induces excess permeability and vascular cell death in diabetic retinopathy (DR). The hypothesis is based on findings that diabetes increases expression of LOX, which is required for the formation and maturation of the BM, and that HG-induced LOX upregulation and over-activation compromises endothelial barrier function. Importantly, inhibition of HG-induced LOX overexpression results in reduced cell monolayer permeability. While LOX is known for its cross-linking activity, LOX propeptide (LOX-PP), released during LOX biogenesis, is known for regulating cell proliferation and survival through modulation of Akt and Erk pathways. Our preliminary data indicates that HG-induced LOX overexpression promotes apoptosis in retinal endothelial cells, and that the process may be exacerbated by LOX-PP, which is upregulated by HG. Furthermore, preliminary data indicates that LOX binds with high affinity to extracellular fibronectin (FN) under HG condition, and interferes with LOX internalization into the cell, a process unique to LOX. Thus, the rationale for the proposed studies is that (i) HG-induced LOX overexpression contributes to capillary leakage, and together with increased LOX-PP promotes apoptosis by modulating Akt and Erk pathways, and (ii) HG-induced increased binding of LOX with ECM proteins, decreases LOX internalization, attenuates negative feedback signaling and thereby promotes LOX overexpression. The proposed studies will be performed using biochemical, molecular, and genetic approaches utilizing cell culture models, diabetic rats, and LOX heterozygous KO mice (LOX+/-). Towards this goal, we have generated LOX+/- mice colonies at our animal facility that are now available for the proposed studies. The specific aims of this proposal are to determine (i) whether inhibition of LOX overexpression and activation prevents apoptosis in retinal endothelial cells in vitro, and reduces vascular cell loss and permeability in diabetic rat retinas (ii) whether the decreased LOX level in LOX+/- mice is protective against diabetes-induced retinal vascular lesions, and (iii) mechanism(s) by which HG induces LOX overexpression and promotes retinal vascular cell loss. Findings from these studies are expected to identify a novel therapeutic strategy for preventing retinal vascular cell loss and capillary leakage, and provide mechanistic insights underlying HG-induced LOX overexpression in DR.